so I played DK up to Creepy Castle and I am now facing a problem of which I don't know if it's caused by the ROM or the Emulator.

As Chunky Kong, there is a "Treehouse", more like a shed, and you have to get invisible so you can take care of the bats, which are normally invulnerable. The easiest way to do this is using your instrument while being invisible. But, invisible or not, I can't use my instrument in this specific room while any other C-Button-Action works. Maybe this is a problem with the controller even though it works fine otherwise?